Low-water alarm



May 24, 1927. F M. ROBY LOW WATER ALARM Fild March 19. 1925 Pigtail 351 W QAQ aftozmzq heat conducting means extends Patented May 24, 1927.

UNITED STATES PATENT OFFICE. V

FRANK 1'1. RGBY, OF CLEVELAN'ILOHIO, ASSIGNOR T HERMAN B. THURSTON, OF

CLEVELAND, OHIO.

LOW-WATER ALARM.

Application filed March 19, 1925. Serial No. 16,826.

claimed in a prior application of Herman B.

Thurston, Sic-rial No. 726,711, filed July 18, 1921, and the particular feature of the invention lies in an improvement in the insulating means for the thermo-responsive element of a low water alarm such as shown in a copending application of Herman B. Thurston, Serial No. 16,627 filed March 19, 1925, in which 1 show a fusible plug normally closing a passage for steam which communicates with the steam space of a boiler and with a signal device such as a whistle. This plug is retained in a housing, adjacent the crown sheet to the fire box. A

plug and this means is insulated by an enveloping jaclret,against the absorption of heat into the water in the boiler, from a point near the crown sheet to a point near the plug. The result is that when the water in the boiler drops to a dangerously low level, the direct heat path to the water from the housing and plug is cut off by the jacket, whereupon heat conducted by the housing accumulates about the plug sufficient'to melt it and cause the alarm to sound. It is to be understood that the particular type of alarm shown is only illustrative of a specific use of my invention. I

The. present invention is especially concerned with constructional changes whereby the improved alarm may be more easily and cheaply manufactured and whereby the efiiciency of the insulating apparatus in connection with the alarm is improved.

The distinguishing features and the mode of operation will become more clear from the description. to follow, which relates to the accompanying drawings wherein I have illustrated the preferred form of my invention. The essential novel characteristics are summarized in the claims.

In the drawings, Fig. 1 is a substantially central longitudinal section through the porfrom the tion of a low water alarm which embodies my invention; Figs. 2 and 3 are transverse sections taken along the lines 2- 2 and 3-3 of Fig. 1.

. Referring to the drawings in detail and indicating the various parts by numerals, 1 is a section of the roof sheet of the boiler and 2 is a corresponding section of the crown sheet. The relative distance between these portions of the boiler is exaggerated by breaking away the radial bolts 3 as shown and bringing the sheets together for better illustrating the invention. As before mentioned, the alarm in general constitutes passages leading from the steam space to a fusible plug and then outward through the boiler wall to a whistle. The passage preferably begins in a cavity 5 ofa combination packing fixture 6 which is in effect a steam dome and which is shown as threaded into the roof sheet at .7. Projecting within the cavity, I have shown a tube 8, the end of which may be suitably spaced apart from the cavity walls in order that a connection is maintained between the steam space and the interior of the tube.

The lower end of the tube is shown as threaded into a bell shaped sleeve 9 which in turn has a threaded connection 10 with an u oper flanged portion 11 of a plug cage 12. assages 13 beginning in an annular groove 14 in this flanged portion 11 preferably communicate with a chamber 15 in substantially the central region of the cage. The lower portion of this chamber may be closed by a heat conducting or fire box plug 17 threaded into the cage at 18 and extending downwardly through the crown sheet and preferably into the fire box as shown. This plug is shown as arranged to be easily removed by reason of the enlargement 20 at its lower end and for this reason the enlargement is preferably provided with angular faces.

Closing the passageway above referred to and extending into the chamber 15, I have shown a removable plug 22 having an angular head,.a normally closed longitudinal opening 23 and transverse openings .24. The upper portion of-the longitudinal opening in the plug may be filled with an easily fusible material such as pure tin or tin alloy as indicated at 25, and it will be noted that by the arrangement shown, direct heat conductivity from the fire space to the plug is had by reason of the plug 17 and the threaded engagement thereof at 18 with the cage.

It is desirable to keep the ten'iperature of the cage surrounding the fusible plug low enough so that the plug will remain solid while there is sufficient water over the crown sheet and so that the cooling etl'ect of water in the boiler when at a safe level will be sure of maintaining this low ten'iperz-iture, l have cut the cage away as shown at 27 leaving simply enough material at this point to provide the desired strength and further to provide walls .for the longitudinal passages 13. The preferred manner of cutting this groove is to cut away the materials as in a lathe as shown in Fig. 2 to substantially the diameter indicated at 28 and afterward mill out the remaining desired amount of mate rial on chords such as 29. During these turning and milling operations, a flange 30 is retained in the central region of the cage as shown producing in effect double cut away portions or grooves 27 and 27 above and below the flange. The lower groove has a double purpose in that it provides an insulation against absorption of heat by the water from the lower or heat conducting portion of the cage and at the same time it tends to throw the heat conducted by this portion of the cage directly toward the fusible portion 25 of the plug.

The flange 30 is adapted to retain the upper end of the insulating casing as by peripheral threads 33 and to further provide for a very water tight joint the casing may be brazed or welded as at 34. The lower end of the casing preferably threaded into the crown sheet as at 35 cutting off any possibility of water connection below the flange 30 which might absorb heat from the body of the cage. The upper portion of the jacket should be made as light as possible consistent with the required strength and corrosion resistance so that when the water level is below the zone of the flange 30. the cooling effect of the water on the cage will be reduced to a minimum. To this end I have shown the thickness of the jacket reduced as by boring out any excess metal above the point 38.

The opening in the crown sheet should be kept as small as possible and I have therefore shown the diameter of the casing reduced in the region of the threads The opening 39 in the jacket is entirely out of contact with the shank of the heat conducting member 17 and preferably has angular faces to provide for screwing the body of the alarm into place in the crown sheet and to facilitate its removal when desired.

In operation, it will be apparent that, so long as the water over the crown sheet is of a depth sufficient to cover the cut away portions 27 even periodically, (as when the water in the boiler is in a surging condition), the temperature of the plug will be kept below the melting point by reason of the slight amount of material between the cut away portion 27 and the fusible plug. That is to say, there will be enough heat drawn from the cage into the water to insure the plug remaining in a solid state.

However, as soon as the water drops below the cut away portion 27 and'stands about the water jacket 32. this heat absorbing effect of the water will be imn'iediately reduced almost to a nullity, and the heat from the tire box will then accumulate quickly in the cage suliiciently to melt the plug 25 before the water has receded in the boiler to a dangerous level below the crown sheet. It will be noted that the amount of metal about the fusible plug necessary to raise to the melting point of tin, after the above conditions obtain, is very slight, which further insures the quick action of the alarm.

When' the plug; melts, steam traverses the passages heretofore described to sound the a.ari'n, blowing the melted particles of the plug upward along a central pipe 37. preferably brazed and threaded into the top of the cage as at and 46 and which may extend through packing 40, a gland a]. and a packing nut 42 to a whistle It will be seenthat I have provided a low water alarm capable of attaining the objects above outlined which maybe very easily and cheaply ,n'ianufactured. The insulating jacket I have made very simple and capable of being easily assembled with the alarm and the boiler and as easily removed therefrom when desired. The water jacket more over serves to hold the fusible plug cage rigid y in place when it is desired to remove and replace the tire box plug 17 and the fusible plug 22 after the alarm has sounded The whole alarm may be very easily and quickly installed in the boiler by first insertthe assembled cage, jacket and tubes through the opening found by the threads 7 then screwing the jacket into place by a wrench engaging the angular opening 3%, and thereafter screwing the plug 17 and the packing fixture 6 into their respective places.

Having thus described my invention, 1 claim:

' 1. The combination with a boiler structure including a fire box and a crown sheet, of a low water alarm, said alarm con'iprising a signal, a member having a passage for conducting steam from the boiler to the signal, a fusible metallic plug normally closing said passage, a cage for housing the plug and forming part ofthe passage, a portion of the cage extending to the tire space and arranged to conduct heat therefrom to the plug, an insulating jacket surrounding the conducting portion of the cage and having a lili closed connection with the cage at one end and a threaded connection with the crown sheet-ofthe boiler at the other, there-being a 2. The combination with a boilerstruc ture including a steam space and a water space, of a low water -alarn1-comprising a member having a passageextending within a boiler, afusible metallic plug normally closing the passage, a housing for the plug portion above the :gen-

having a cut awav .eral region of the plug .for affordinga short radiating path between water in the boiler and the plug when the water level is above the plug, and a jacket contacting with the housing adjacent the cut away portion and separated therefrom throughout the remainder of its length, whereby an insulated chamber is formed between the housing and the water space of the boiler when the water level drops below the cut away portion.

8. The combination witha boiler struc ture including a fire space and a crown sheet, of a low water alarm comprising a member having a passage extending within the boiler, a fusible metallic plug normally closing the passage, a cage surrounding the plug, a jacket in intimate contact with the cage in the region of the plug, skirting the cage and in threaded engagement with the crown sheet, and a heat conducting member extending from the cage through one end of the jacket and in spaced relation thereto at the same end, said heat conducting member projecting into the fire space for conducting heat therefrom to the plug.

at. The combination with a boiler structure including a fire space and a crown sheet, a low water alarm comprising a member having a steam passage extending within the boiler, a fusible metallic plug normally closing the passage, a member surrounding the plug, a jacket in threaded engagement with the member in the region of the plug, spaced apart from the member below the plug and in intimate engagement with the crown sheet and a heat conducting member extending from the plugsurrounding member to the region of the crown sheet for conducting heat from the fire space to the plug.

5. The combination with a boiler structure including a fire space and a water space, of a low water alarm, said alarm comprising a signal, a member having a steam passage extending within the boiler, a fusible metallic plug closing the passage, a passage communicating with the plug and extending to a signal, a cage for housing the plug having a heat conducting connection with the fire space and being provided with separated flanged portions above the general region of the plug, a peripheral groove of uneven depth between the flanged portions, and a plurality of longitudinal passageways forming a portion of said steanr-passage extending from one of the flanged portions through the other :past the groove and in communication with the plug and meansin intimate'contact withone of the flanges for insulating the :lower portion of the cage fro'm' the water spaceof'the boiler.

6, The combination with a boiler structure including a water space, of a lowiwater alarm,-a memberhaving a .passageextending within the boiler, a ifivlsible metallic :plug normally closing :the passage, a housing :for the plugzhaving flanges formed by grooves ,in :the general region (of the plug, a jacket in intimate ,contact with .the 'jhousing ,at one of the flanges and separated therefrom throughout the remainder of its length, whereby an insulating chamber is formed between the housing and the water space of the boiler below the Zone of the metallic plug while intimate contact of the water in the boiler is had with the casing between the flanges.

7 The combination with a boiler structure including a fire space, a steam space, a water space and a crown sheet, of a low water alarm, a member having a passage extending from the steam space of the boiler to the water space including a threaded conduit member, a fusible metallic plug in the region of the water space normally closing said passage, a cage for housing said plug, a pair of threaded flanges carried by the cage, one being engaged by the threaded conduit member, a heat conductin member extending from the cage to the fire space, a acket insulating said conducting member and in threaded engagement with the other flange and in intimate contact with the crown sheetof the boiler whereby, when water in the boiler falls'below both flanges, the plug may be melted by the heat from the fire box.

8. The combination with a boiler structure including a fire space, a steam space and a water space, of a low Water alarm comprising a signal, a member having a passage leading into the water space of the boiler and communicating at'its respective ends with the steam space of the boiler and the signal device, a fusible plug normally closing said passage, a housing for supporting the plug and carrying a heat conducting member which extends to the fire space, a flange carried by the housing near the region of the plug, a water tight jacket in engagement with the flange and otherwise spaced apart from the housing, and means associated with the flange whereby sufiicient heat conducted by said member is directed toward the fusible plug to melt it when the level of the water in the boiler drops below the zone of-the flange.

9. In combination with a boiler structure including a fire box and a crown sheet, of

15 and in the region of the crown sheet. thereof,

a thermo-responsive element carried by the cage member, a signal device externally of the boiler and arranged to be actuated consequent upon suli icient heating of said element, said cage having a portion thereof reducedin cross-section above the region of said element, and a tubular insulating member spaced apart from the cage substantially the entire length thereof and in intimate relation with the cage immediately below the reduced portion for preventing water contact with the cage.

In testimony whereof, I hereunto aifix my signature.

FRANK M. ROBY. 

